Chemicals used to cure beef jerky, salami, hot dogs, and other processed meat snacks may contribute to mania, an abnormal mood state characterized by hyperactivity, euphoria, and insomnia, according to a new study.

The study, which appears in the journal Molecular Psychiatry, while not designed to determine cause-and-effect, did find that people hospitalized for an episode of mania were three times more likely ever to have eaten nitrate-cured meats than were people without a history of a serious psychiatric disorder. Experiments in rats by the same researchers showed mania-like hyperactivity after just a few weeks on diets with added nitrates.

Mania, a state of elevated mood, arousal, and energy that lasts weeks to months, is generally seen in people with bipolar disorder.

While a number of genetic and other risk factors have been linked to manic episodes that characterize bipolar disorder and other psychiatric conditions, those factors have been unable to explain the cause of these illnesses. Researchers are increasingly looking for environmental factors, such as diet, that may play a role.

The new study adds to evidence that certain diets and potentially the amounts and types of bacteria in the gut may contribute to mania, the researchers say.

“Future work on this association could lead to dietary interventions to help reduce the risk of manic episodes in those who have bipolar disorder or who are otherwise vulnerable to mania,” says Robert Yolken, professor of neurovirology in pediatrics at the Johns Hopkins University.

Meat and mania

Mania, a state of elevated mood, arousal, and energy that lasts weeks to months, is generally seen in people with bipolar disorder, but can also occur in schizoaffective disorder. Manic states can lead to dangerous risk-taking behavior and can include delusional thinking. Most of those affected experience multiple hospitalizations.

“We looked at a number of different dietary exposures and cured meat really stood out.”

Bipolar disorder affects an estimated one to three percent of the US population and costs an estimated $25 billion a year in direct health care costs, according to a study in the Journal of Affective Disorders.

Yolken, trained as an infectious disease expert, was originally interested in whether exposure to infections such as viruses transmitted through food might be linked to psychiatric conditions. He and colleagues collected demographic, health, and dietary data on 1,101 individuals with and without psychiatric disorders.

Unexpectedly, among people who had been hospitalized for mania, the team found a history of eating cured meat before hospitalization 3.5 times higher than in the group of people without psychiatric illness. Cured meats were not associated with a diagnosis of schizoaffective disorder, bipolar disorder in people not hospitalized for mania, or in major depressive disorder. No other foods had a significant association with any of the disorders.

“We looked at a number of different dietary exposures and cured meat really stood out,” Yolken says.

Nitrates have long been used as preservatives in cured meat products and have been previously linked to some cancers and neurodegenerative diseases. The dietary survey did not ask about frequency or time frame of cured meat consumption, so the researchers couldn’t draw conclusions about how much cured meat may boost one’s risk of mania, but Yolken hopes future studies will address this.

Altering rat brains

To get at the roots of the association, Yolken collaborated with researchers studying the impact of nitrates on rats.

They divided otherwise healthy rats into two groups: one received normal rat chow, and the other both normal chow and a piece of store-bought, nitrate-prepared beef jerky every other day. Within two weeks, the rats eating jerky showed irregular sleeping patterns and hyperactivity.

Next, the team worked with a Baltimore beef jerky company to create a special nitrate-free dried beef. They repeated the experiment, this time giving some rats the store-bought, nitrate-prepared jerky and others the nitrate-free formulation. The animals that ate the nitrate-free meat behaved similarly to a control group, while the animals that consumed the nitrates once again showed sleep disturbances and hyperactivity similar to that seen in mania.

The results were then replicated with a specially formulated rat chow that had either nitrate added directly to the chow, or no nitrate.

The amount of nitrate consumed on a daily basis by the rats—when scaled up to the size of a human—was equivalent to the amount a person might eat for a daily snack, such as one beef jerky stick or hot dog.

“We tried to make sure the amount of nitrate used in the experiment was in the range of what people might reasonably be eating,” Yolken says.

When the group analyzed the gut bacteria of the rats, they found that animals with nitrate in their diet had different bacteria in their intestines than the others. The animals also had differences in several molecular pathways in the brain that have been previously implicated in bipolar disorder.

While occasional cured meat consumption is unlikely to spur a manic episode in most of the population, Yolken says the findings add to evidence that multiple factors contribute to mania and bipolar disorder.

Funding for the research came from the National Institute of Mental Health and the Stanley Medical Research Institute. Additional researchers contributing to the work came from Johns Hopkins, Sheppard Pratt Health System, Purdue University, and Mobtown Meat Snacks.